I'll grab a pic of an old beetle culture in a bed of diatomaceous earth. You can see a concentration of mites around the lip of the lid and a distinct ring of dead mites on the DE. I have noticed that the lid seals are not perfect so I'm pretty sure there are gaps a mite can get through. DE is awesome though - I have not had any booms since using it. Only problems I have encountered are with my really old bean beetle cultures.

I doubt they are able to get in a snapped on lid either. Mites crawl. Mites climb. They are on the lip and outside of the cups and get inside when we feed out ect. They are not getting thru the fabric or past a well snapped lid.

Mites are crawling all around any area where cultures are kept. They get out when lids are opened for feeding out...funnels be damned. Wiping be damned. SOME amount of free-crawling mites are always present around cultures due to opening them to feed out.

It would take a serious experiment to prove that they are getting out of the lid and fabric....on their own.

Well I'm just recounting what I've seen, and how it's impacted my FF and BB culturing. Recently I started keeping BB, so I'm new and not familiar with the culture cycles. I also don't feed off them that regularly yet. They are in their own culture box, as are all species of FF I keep. Each box is lined with ~1" of DE.

In November I had a mite problem in my BB cultures. There were 11 cultures - 4-3-4 orientation - with no cultures touching. One by one the three in the middle developed mite infestations as they hit the three month mark; I had not opened or moved the middle ones for that month. They each developed a distinct ring of mite carcasses around their base as the mites died exiting the cultures. The darkest part of the rings (assuming the deepest pile of carcasses) were right next to the culture, and the ring lightened further away from the cup wall. There were concentrations of mites on the fabric lids and the lip of the cup, both inside and out. Not scientific proof, but the implication was the mites were in the culture, boomed, and got out...three times. Now I sift out the bean beetle carcasses and waste periodically but it's enough for me to strongly suspect these lids are not mite proof, and that additional steps are required to prevent and isolate cultures from cross contaminating.

Gee I dunno Jim. As much as I like to process your observations above, I still think that if any lid is taken off whatsoever - all bets are off as far as mite origin is concerned.

What we know:

Mites are in or around almost ALL foodstuffs - grain like foods. Heck mites are on US right now. On our face. On our eyebrows ect. They are crawling all over our yard. Our pool. Our pets, ect. They are everywhere. Always.

They climb.

They tend to congregate on edges and in cracks. This is why FF cultures are better stored on flat trays and not in cubicles or cabinets or in enclosed boxes.

When they are found dead - all fluffy and brown and 'yeasty' (heh, made that term up just now) it is still IMO, very much a mystery if they were COMING or GOING.